The described aspects relate generally to wireless communication systems. More particularly, the described aspects relate to techniques for uplink transmission management in wireless communications.
Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, time division synchronous code division multiple access (TD-SCDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems.
These multiple-access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). LTE is designed to support mobile broadband access through improved spectral efficiency, lowered costs, and improved services using OFDMA on the downlink, SC-FDMA on the uplink, and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. These improvements may also be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.
By way of example, a wireless multiple-access communications system may include a number of base stations, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UEs), wireless devices, mobile devices or stations (STAs). A base station may communicate with the communication devices on downlink channels (e.g., for transmissions from a base station to a UE) and uplink channels (e.g., for transmissions from a UE to a base station).
As cellular networks have become more congested, operators are beginning to look at ways to maximize the use of available network resources. One approach may include utilizing an unlicensed or shared spectrum (e.g., 5 Giga Hertz (GHz) band) to schedule traffic between the base station and the one or more communication devices. As referenced herein, a wireless communications system that adapts LTE air interface to operate in unlicensed or shared spectrum may be referred to as an LTE-U system or a license-assisted access (LAA) system. The unlicensed spectrum may be employed by cellular systems in different ways. For example, in some systems, the unlicensed spectrum may be employed in a standalone configuration, with all carriers operating exclusively in an unlicensed portion of the wireless spectrum (e.g., LTE Standalone). In other systems, the unlicensed spectrum may be employed in a manner that is supplemental to licensed band operation by utilizing one or more unlicensed carriers operating in the unlicensed portion of the wireless spectrum in conjunction with an anchor licensed carrier operating in the licensed portion of the wireless spectrum (e.g., LTE Supplemental DownLink (SDL)).
Due to respective requirements regarding operations in licensed spectrum and unlicensed or shared spectrum, uplink transmissions are generally subject to a listen-before-talk (LBT) approach. That is, when a communication device (e.g., UE or STA) has uplink data for transmission, the communication device may perform a channel check (e.g., clear channel assessment (CCA) or extended clear channel assessment (eCCA)) prior to transmitting any data on the uplink channel. If the result of the channel check indicates that a channel is available for the uplink transmission, i.e., the channel is clear for use and the channel check succeeds, the communication device may then accordingly transmit uplink data. However, if the result of the channel check indicates that the channel is unavailable for the uplink transmission, i.e., the channel is currently busy and the channel check fails, the communication device typically may have to wait until some later time resulting in uplink transmission delays. Other aspects of operations in licensed spectrum and unlicensed or shared spectrum that may cause delays in uplink transmissions are related to the use of hybrid automatic repeat request (HARD) operations.
Therefore, there is a need to provide mechanisms for uplink transmission management that are suitable for wireless communications in an unlicensed or shared spectrum.